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Photolithographically Defined Optical Cooling Devices for Electronic Cooling Plane Applications


TECHNOLOGY AREA(S): Info Systems, Sensors, Lectronics 

OBJECTIVE: The objectives of this topic are to invent a device that can be manufactured in an arrayed geometry using whole wafer lithography techniques wherein anti-Stokes optical upconversion can produce net cooling at each device and wherein well-verified physics allows the upconverted photons to be caused to flow preferentially in predefined directions away from the localized heat sinks, independent of the local electronic temperature distribution. 

DESCRIPTION: In most non-elemental solids, there are ground and excited state energy bands of the electrons that contain sub-bands separated by the energies of thermally excitable phonons of the crystal lattice. If one of the ground state electrons absorbs a photon that promotes it to such an excited state band and then it subsequently also absorbs a phonon, and if the excitation decays by emitting a photon, then the new photon will have more energy than the originally absorbed one. This is called the anti-Stokes process and the newly emitted photon will be blue shifted. The ability of this process to deliver net cooling of the solid is determined by the branching ratio between the emission of the upconverted photon and all other decay paths of the excitation and the likelihood that the upconverted photon will escape from the local environment which, for applications, we wish to cool. Most demonstrations of this physics have to date been done in bulk glasses where the re-radiated photons leave the object being cooled isotropically. Even if such devices could be made into a planar geometry suitable for incorporation in a 3D stack of electronics, this isotropy would mean that the vast majority of the upconverted photons would have to pass through the devices we wish to cool in the adjacent planes, many would be absorbed there, and the net cooling of the electronics would be dramatically reduced. What is needed is a way to cause the anti-Stokes photons to leave their point of origin headed in a controllable, specific direction and then to follow that path to a sink point which allows them to be removed from the 3D stack in a convenient manner, such as via a low loss optical fiber. Fully optimized versions of such cooling planes would allow vertical co-fabrication of the cooling structures and the active components being cooled, but for the purposes of the Phase I proposal of this topic it will be sufficient to define a device geometry and select materials to demonstrate net optical cooling from a clearly defined starting temperature, produce a technical approach that works to reduce the technical risk of the proposed device, and argues how the integratable cooling plane would be built if the individual device is successful in the materials chosen. If the approach proposed will be applicable to only a portion of the entire range of circuit operating temperatures of ~4K to 400K (-289C to +125C), those limitations should be discussed in the proposal. 

PHASE I: The purpose of the Phase I effort is to refine the device concept presented in the initial proposal and amplify the supporting scientific evidence about the behavior of the selected materials to the point where the Phase II decision can be made with realistic expectations of the performance possible at the end of Phase II base. For example, if the original proposal indicates there are two or three candidate materials for use in the cooling volume, the Phase I should determine which is in fact most promising. Likely fabrication issues for the cooling devices should be explored. Detailed multi-physics simulations might be attempted. Demonstration of the method(s) proposed for controlling the upconverted photon outflow are very desirable. Fabrication of a first prototype single device and proof it cools would be ideal. The preliminary Phase II proposal prepared at the end of Phase I should include a discussion of the factors that could limit the energy efficiency of the chosen design and what could be done to mitigate these limits if Phase II is awarded. 

PHASE II: The Phase II effort will have four goals: optimization of the thermal performance of the chosen single cooling device, planning the integration of a set of such devices into a first array/cooling plane demonstrator, and fabrication and test thereof, followed by further optimization. The first goal must be completed in the base portion of the award since the first option must be cost shared by a user who wants to utilize this method of cooling and they must be convinced it is no longer "high technical risk" work. Further follow on efforts will require user financial support and hence are expected to work toward the sponsor's specified temperature range, thermal lift, and specific application, and conceivably could become classified if the application is. 

PHASE III: The central concept of this topic will, if successfully realized, be considered as enabling, have many different uses, and ought to qualify as "Dual use" for ITAR purposes. The military applications should range from cooling wiring and possibly power amplifiers in high-power transmitters (used for surveillance and electronic attack) to the sensing of chemical, biologic, or radioactive weapons at long wavelengths, to the provision of cryogenic cooling for electronics dependent on low temperature environments. However, the application of local or general cooling, integrable with 3D stacked electronics, has wide applicability in the consumer electronics fields where heat removal often dictates maximum processor density for laptops and forces strategies such as sequential depowering of circuit blocks to allow sufficient cooling time for the stack not to over-heat and-or catch fire. 


1: Boriskina, S. V., Tong, J. K., Hsu, W. C., Liao, B. L., Huang, Y., Chiloyan, V. and Chen, G. "Heat meets light on the nanoscale", Nanophotonics 5 (#1), pp. 134-160, June 2016. (Open Access)

2:  Nemova, G. "Laser cooling of solids",

3:  Ruan, X. L. and Kaviany, M. "Advances in laser cooling of solids", Journal of Heat Transfer 129 (#1), pp. 3-10, Jan. 2007,

KEYWORDS: Laser Cooling; 3-Dimensional Packaging; Anti-Stokes Radiation; Solid State Cooling; Cryogen Free Cooling; Reradiation Branching Ratio 


Deborah VanVechten 

(703) 696-4219 

Janet Jensen 

(410) 417-3320 

Timothy Haugan 

(937) 320-5852 

Marc Ulrich 

(919) 549-4319 

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